This invention relates to a method for detecting the position of a fuel injection quantity adjusting member of a fuel injection pump and an apparatus for carrying out the method.
In general, a fuel injection pump is provided with a rack sensor (position detector) for detecting the position of a control rack (fuel injection quantity adjusting member), so that the position of the control rack is feed-back controlled or the fuel injection timing is controlled in accordance with a detection signal from the rack sensor.
Conventional rack sensors each comprising a differential transducer have individual difference in output characteristic. Moreover, when a fuel injection pump is attached to a diesel engine, the position of the control rack is appropriately adjusted for each diesel engine, so that a prescribed rated output can be obtained at a prescribed rated speed of rotation. For this reason, if the output of the rack sensor should be used as it is, it would occur that the detected position of the control rack does not correspond to a load condition of the diesel engine.
Therefore, in the device disclosed in Japanese Patent Publication No. 8620/1992, the output characteristic of a rack sensor is calculated based on a prescribed low load side reference position at the time of idling operation of the diesel engine and a prescribed high load side reference position in a predetermined region of rotation at the time of full load operation of the diesel engine, and output voltage (detected position) of the rack sensor at the time of idling operation and full load operation, and the output voltage (detected position) of the rack sensor is corrected based on this output characteristic.
However, since the position of the control rack is greatly affected by irregularity of friction, etc. of the diesel engine when the diesel engine is in an idling state, an actual position of the control rack at idling of the diesel engine is usually adjusted for each diesel engine, so that a target speed of rotation can be obtained for each diesel engine. For this reason, even if an output characteristic of the rack sensor is obtained through calculation in the manner mentioned above, the output characteristic of the rack sensor thus obtained becomes different from a true output characteristic after adjustment. As a consequence, it gives rise to such a problem that the corrected detected position does not correspond to the load condition of the diesel engine.
Moreover, there is also such a problem that since the position of the control rack at idling is always slightly varied, a correct output voltage of the rack sensor is difficult to obtain.